Got home from the trustees meeting last night to a glorious clear sky. On a Monday? Really?
I made an aperture mask for my dob over the weekend and was itching to try it out. The idea behind the mask is that on bright targets cutting out a bit of light and diffraction from the secondary struts should improve clarity, even though the aperture is reduced (350 to 160 in this instance).
And so after failing to resist temptation I was setup by 11:20:
Jupiter: Disappeared behind neighbors house. Need to catch it in the gap between house and apple tree 1.
Saturn: Seeing dreadful without mask: boiling away with no clarity at all. With the mask: same but dimmer. Hmmm.
Pluto: Spent ages looking for this. Definitely in the right place. Pluto formed a triangle asterism with two other faint stars. I upped the magnification to dim the sky glow and there was definitely something there. Wobbled the scope – that helped. Averted vision- didn’t make much difference. So- I’ve looked at Pluto but not seen it! Beginning to regret doing this on a work night…
Jupiter again. Behind apple tree 1. That moved quick! Damn!
Izar: At last- some success. Successively improved views moving from Baader zoom to binoviewers to adding aperture mask. In the final view the stars were pinpoint sharp and well separated with the companion showing a lovely blue.
Double double: the same experience. The 2 pairs were easily separated in all 3 configurations, but the binoviewers plus aperture mask gave the best view.
M13: Too dim for the mask, the best view was in the binoviewers- resolving all the way to the core and seemingly spherical, even though at that distance you don’t really have depth perception!
Jupiter again: Gotcha! Just before it snuck behind apple tree 2… Definitely a better view with the aperture mask- slightly dimmer but with much more clarity. 6 bands plus the GRS were clearly visible, with some detailing on the bands, plus the moons spread out as clear disks 3 to one side and one on the other.
Well worth the fatigue today!
Very pleased with the aperture mask- it’s not often an astro upgrade is almost free. It’s only really good for bright objects and with the binoviewers I had to velcro 4kgs onto the bottom of the tube to balance it- bit well worth the hassle!
After hearing about the rapid set up and simplicity of a Dobsonian mount for casual observing, I thought I would investigate how to get one as an alternative to my EQ5. Strange that these mounts cannot be bought separately, except at Orion Optics UK, where I was quoted a high price. This set me on the DIY route.
I decided that I wanted the capability to adjust the tube axially (for balancing) and rotationally (for comfotable viewing position), as with the EQ5.I also wanted easy transfer of the tube between Dob and EQ5 (no tools needed). After a week of research, I settled for a hybrid that included a features from this article: http://www.scopemaking.net/dobson/dobson.htm, The Sky at Night articles in Dec 2014 and Jan 2015 and the Orion Optics design. Originally, I was going to design the rings and dovetail bar to be interchangeable, but when a set became available I settled on a separate ring set for each mount.
I won’t go into detail about the build/assembly but show various stages in pictures. The main stages are; 1.mods to the ring set, 2.cutting, shaping and painting, 3.bearings and the 4.optional brake. Anyone who wants more detail please contact me.
1. Modify ring/rails assembly.
Trunions: PVC 160mm pipe plugs (Buildbase, Newhall, Swadlincote). Protect bearing surface with masking tape. Locate centre and fix to bar with 1/4″UNC fasteners (Pugh & Sanders Ltd Burton on Trent).
Shape and fit 2nd ‘rail’ from 10mm plywood. Fix to rings with 1/4″ csk head screws. Locate trunion on centreline in same position exactly as other trunion.
Trial fit completed ring/rail assembly to scope
2.Cutting, shaping and painting frame
I used 18mm mdf for the base and sides and 10mm plywood for the front, back, rail and accessory tray. Use plastic fixing blocks and screws to hold everything together. No adhesive needed. Take basic dimensions from the article referenced above, except width of front and back, noting that alt bearing box is not needed and friction brake needs to be included.
Mark out parts using trammel to draw circular base.
Cut with jigsaw and smooth with rasp and glasspaper
To obtain width of front and back, measure distance between trunion flanges and add 10mm.
Use plastic fixing blocks to assemble, drill through upper base and screw to frame, bolt to lower base, trial-fit scope assembly. If all goes pear shaped, use as a ‘lazy-susan’ coffee table!
Trial fit 3 feet 120° apart.
Use jigsaw and ripsaw to cut holes to reduce weight and improve appearance.
Hang from washing line for painting – 2 coats minimum. Have a coffee between coats!
For altitude bearing use two 2mm thick ptfe sheets, drilled and countersunk in centre for small csk head screw.
For azimuth bearing use 3 Magic Glides (Wickes) spaced 120° apart within 300mm circle .
Use M10x60mm carriage or ordinary bolt and M10 Tee Nut (Amazon or ebay) inserted upside down for pivot in lower base. Tighten so it will not fall out or turn when M10 Nyloc nut is tightened.
For upper bearing use 12″ vinyl record (grooves make for low friction). To form a good bearing for the bolt in the upper base use a brass10-15mm reducer plumbing fitting (Wickes) drilled out to 10mm. Secure bases with oversize washer, spring washer and M10 Nyloc nut. Tighten only enough to take up slack.
Small spacers are needed to prevent sideways movement of scope assembly. Spacers are squares of ptfe fastened with small screw and spring washer fitted between side and flange of trunion. Trial fit to to gauge the spacer size and position of spacers.
4, Friction Brake Feature – Optional
This feature prevents the scope moving if the assembly becomes out of balance, although there is the option to slide the tube axially.
Attach another strip of ptfe to top of curved section of brake. Attach small hinges between brake and side using small 90° brackets to allow screwing into face of wood – mdf will split if screwed into edge! Attach a ‘Brighton sash window catch’ (satin chrome finish from Screwfix) such that it can be released to allow the scope to be lowered into place and tightened to stop movement or lock the scope. Fit accessory tray to front and hooks to sides for clipboard, glasses etc. Extension legs can be used if elevation is low or if the ground is long wet grass. To make carrying more comfortable, fit a length of 12mm soft clear plastic hose cut lengthways to upper curve of the front.
I had great fun making this but have used it only briefly to observe the Moon and was pleased the way it moved…but I still like the fine control provided by my EQ5 control cables. Now how can I add this feature to the Dob…?
Next stage of my video eyepiece construction completed today, ready for testing hopefully tomorrow evening which is predicted to be clear.
In the first photo, the components are connected and working. In the second photo, I have assembled everything into single unit. The photo below shows the video eyepiece with lens on it rather than 1.25 inch telescope adapter.
Roger suggested this project at a RAG meeting and kindly sent me a list of required components. The project is to produce an electronic eyepiece based on PD camera with small screen next to it so that observers can get the benefit integrated video images with their improved limiting magnitude over the eye at a glass eyepiece whilst retaining the “At the telescope” experience and not requiring user to carry lots of kit into the field. The mantra is simple, easy and effective, with the visual observer in mind at all times. The components required include the PD camera, which I already had, 7 inch LED screen, a 12V to 5V converter, various connectors and small 12V battery to power it all.
Main task is to add in converter and connect all so that single 12V power connection with power both PD camera and the 5V screen as well.
I successfully achieved this today. Next step will be shrinking it all down into a neat package and working out how I am going to attach the screen to the PD camera.
After some discussion with Andy T on the benefits of a laser pointer for finding objects, I decided to get one of these. The laser and the bracket are yet to arrive but the extra shoe needed to mount it to the tube, ordered from Harrison Telescopes, arrived in 3 days. This is now fitted with the M4 countersunk screws and black nuts supplied. I will outline the method I used and tools needed, for comparison with Andy’s adhesive-based method (10 March) so you can decide which to use.
1. Make sure you think hard before you decide on the location; drilled holes are permanent. I placed mine about 20mm from the finder-scope shoe, to match the gap between it and the focuser base.
2. Attach masking tape to the area where it is to be attached.
3. Rest the tube horizontal up against a firm support with the focuser aperture above the area to be drilled, to prevent swarf/cuttings getting in. Also, I put newspaper directly under the drilling area to catch any cuttings and masking tape along the inner edge of the stiffener on the end of the tube. Time taken in preparation is well worth it. See the photo below. I would not advise doing this task with the tube in the mount.
4. Mark lines on the masking tape and use the shoe as a template to mark the locations of the two holes.
5. Check that the holes will clear the reinforcing plate (if fitted) inside the tube used for the finder-scope shoe.
6. Tubes are made of thin steel, work-hardened by the rolling process, so sharp drills are essential. Start with a small size drill, say 2.5mm and work up, in steps of 0.5mm, to 4mm diameter. This minimises the force needed to break through initially and subsequently to increase the hole size. Small drills break easily so do not apply too much force, have only a short length of drill protruding from the chuck and try to align the drill radially to the tube.To make sure the drill chuck could not touch and mark the tube, I pushed a rubber tap washer onto the drill, masking tape alone is not thick enough. Make sure you are in a comfortable position and able to control the pressure applied by the drill.
7. After drilling one hole, loosely attach the shoe and check the marked location of the 2nd hole.
8. If the 2nd screw will not insert, increase the hole size of one hole, or both if needed, to 4.5mm. Mine were fine with 4mm diameter.
9. Remove masking tape and the paper inside the tube and attach the shoe. I used a small spanner (shown in photo) to hold the nuts while tightening. Take care not to shear the screws as they have a small cross-section and not to scratch the black paint inside the tube.
Once the bracket and laser arrive I will post a photo of the finished assembly, soon I hope!
Have now fitted bracket and laser but not used it yet. It was quite a loose fit into the shoe dovetail (left in view below) so needed a small aluminium shim. The SW finder bracket is not a brilliant fit either but at least it tightens up before the clamp screw runs out of thread. I think it looks the part at least (see below).
Total outlay for all 3 parts was about £25, all bought separately off ebay.
My trusty and well used Orion 10″ Dobsonian telescope does not have Sky Watcher style finder scope shoes – a nuisance as I would like to use a finder scope with it and also attach my heated laser finder device which has Sky Watcher style finder bracket.
So today out came the glue gun and I attached two finder shoes to the tube. If the glue gun turns off with time not to be strong enough then I will bolt them on but hopefully this won’t be needed as not much weight on them.
The other advantage of using the glue gun initially is that I can change position of the finder shoes if it turns out they are not in the best place in practice.
I chose a rather cold day to do this!
OK so in the next picture it looks a mess. However, once the glue has cooled I will then be able to tidy it up and I would rather put a bit more glue on so that my stuff does not fall off the scope, including my bargain from the Practical Astronomy Show – right angled 9×50 finder scope with illuminated eyepiece for only £45, which I bought especially to put on this scope!
The storm on Sunday night blew off a large patch of the roofing felt on my log cabin observatory in Lichfield. I am very grateful to the help of Damian and Rhys last night, as we struggled against the wind to put a temporary covering over the cabin. This involved cutting down a tarpaulin from Screwfix to appropriate size in the dark and wobbling about on a step-ladder as we tacked it on. We discovered that the underside was a better colour so we installed it upside-down!
Now I need to buy some proper roofing felt and do it properly……
NB Double doors are to allow the 16″ Dobsonian on its castors to be rolled out onto the lawn.
Here are another couple of snapshots from the video electronic eyepiece screen, (see https://roslistonastronomy.uk/video-electronic-eyepiece-image-intensifier) this time the M41 cluster as well as M42. It is quite difficult to get a decent snapshot with a camera due to it being tricky to get the exposure right. I have also found that for visual observing in the dark, it is best to turn down the brightness and contrast as far as it will go on the monitor.
It is probably worth-while comparing these with the processed images from from a few minutes exposure with EXACTLY the same kit (plus a PC, of course) from EXACTLY the same location. (the window-sill). Both methods have their place, of course! Perhaps unsurprisingly, the clusters come out best.
By the way, given some recent discussions, the M42 image is a composite of 4 exposures